ORIGINAL COMMUNICATION Anatomic Pattern of the Terminal Branches of Posterior Interosseous Nerve SADAN AY, 1 * NIHAL APAYDIN, 2 HALIL ACAR, 2 METIN AKINCI, 1 AHMET PISKIN, 3 IBRAHIM TEKDEMIR, 2 AND ALAATTIN ELHAN 2 1 Department of Hand Surgery, Ankara Hand Surgery Center, Ankara, Turkey 2 Department of Anatomy, Faculty of Medicine, Ankara University, Ankara, Turkey 3 Department of Orthopedics and Traumatology, Faculty of Medicine, Ondokuz Mayis University, Samsun, Turkey To understand the lesion of the terminal branches of posterior interosseous nerve (PIN), an anatomic study was carried out. Thirty adult cadaver arms were dissected and the anatomic pattern of the nerve was documented. The distance between the point at which the nerve divides into branches and the distal edge of the supinator were measured, as well as the length of each nerve branch to its muscle-entering sites. The number of branches innervat- ing each muscle was recorded. It was found that the PIN was branching to multiple short branches and a single deep long branch after leaving the supinator muscle with great mor- phometric and schematic variances. Clin. Anat. 18:290–295, 2005. V V C 2005 Wiley-Liss, Inc. Key words: terminal branches; PIN; anatomic pattern; partial lessons INTRODUCTION The radial nerve bifurcates into the superficial sensory branch and the deep branch posterior inter- osseous nerve (PIN) at the level of elbow joint. The PIN enters and passes between the two heads (superficial and deep layer) of the supinator as one bundle. At the distal level of supinator, it divides into bundles that are known to be the terminal branches that have been referred to separately, by different authors as short and long branches (Allbritten, 1946), medial and lateral branches (Mayer and Mayfield, 1947), superficial and deep branches (Spinner, 1972), and descending branches of PIN (Sunderland, 1978). Although the proximal anatomy of the PIN has been reported in numerous anatomical studies (Spinner, 1968; Fuss and Wurzl, 1991; Prasartritha et al., 1993; Rath et al., 1993; Thomas et al., 2000), there are few reports for the anatomy of terminal branches of PIN (Spinner et al., 1988; Elgafy et al., 2000b). Although some studies focused on the order of the terminal branches of the PIN (Sunderland, 1978; Abrams et al., 1997; Branovacki et al., 1998), others were related to the terminal sensory branch of the PIN (Dellon and Seif, 1978; Carr and Davis, 1985; Waters and Schwartz, 1993; Elgafy et al., 2000a). The anatomic location of the terminal sen- sory branch of the PIN is constant in the deep radial aspect of the fourth dorsal compartment and is gen- erally used as a donor graft for digital nerve repairs, or during denervation of painful wrist problems. It has been reported that the traumatic or non-trau- matic lesions of terminal motor branches of the PIN end up as isolated drop thumb deformity (Suematsu and Hirayama, 1988; Hirachi et al., 1998; Hirayama and Takemitsu, 1998), isolated drop fingers (Cravens and Kline, 1990; Hirachi et al., 1998) , and the sign of horns (Spinner et al., 1998; Leechvavengvongs et al., 2001). Detailed anatomic knowledge of the terminal motor branches of the PIN is required for a correct diagnosis and surgery and most of the studies did not *Correspondence to: Dr. Sadan Ay, Ankara El Cerrahi Merkezi, Mesrutiyet Cad. 32/4, 06640-Kizilay, Ankara, Turkey. E-mail: sadanay@tr.net Received 9 April 2004; Revised 7 July 2004; Revised 22 September 2004; Accepted 18 November 2004 Published online in Wiley InterScience (www.interscience.wiley. com). DOI 10.1002/ca.20114 V V C 2005 Wiley-Liss, Inc. Clinical Anatomy 18:290–295 (2005)